[Qemu-devel] [PULL 2/2] dirty-bitmap: fix double lock on bitmap enabling

[John Snow <jsnow@redhat.com>]

From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

Bitmap lock/unlock were added to bdrv_enable_dirty_bitmap in
8b1402ce80d, but some places were not updated correspondingly, which
leads to trying to take this lock twice, which is dead-lock. Fix this.

Actually, iotest 199 (about dirty bitmap postcopy migration) is broken
now, and this fixes it.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-id: 20180625165745.25259-3-vsementsov@virtuozzo.com
Signed-off-by: John Snow <jsnow@redhat.com>
---
 block/dirty-bitmap.c           | 3 ++-
 migration/block-dirty-bitmap.c | 4 ++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/block/dirty-bitmap.c b/block/dirty-bitmap.c
index 93744b3565..c9b8a6fd52 100644
--- a/block/dirty-bitmap.c
+++ b/block/dirty-bitmap.c
@@ -250,8 +250,9 @@ void bdrv_enable_dirty_bitmap_locked(BdrvDirtyBitmap *bitmap)
 /* Called with BQL taken. */
 void bdrv_dirty_bitmap_enable_successor(BdrvDirtyBitmap *bitmap)
 {
+    assert(bitmap->mutex == bitmap->successor->mutex);
     qemu_mutex_lock(bitmap->mutex);
-    bdrv_enable_dirty_bitmap(bitmap->successor);
+    bdrv_enable_dirty_bitmap_locked(bitmap->successor);
     qemu_mutex_unlock(bitmap->mutex);
 }
 
diff --git a/migration/block-dirty-bitmap.c b/migration/block-dirty-bitmap.c
index 3bafbbdc4c..477826330c 100644
--- a/migration/block-dirty-bitmap.c
+++ b/migration/block-dirty-bitmap.c
@@ -511,7 +511,7 @@ void dirty_bitmap_mig_before_vm_start(void)
         DirtyBitmapLoadBitmapState *b = item->data;
 
         if (b->migrated) {
-            bdrv_enable_dirty_bitmap(b->bitmap);
+            bdrv_enable_dirty_bitmap_locked(b->bitmap);
         } else {
             bdrv_dirty_bitmap_enable_successor(b->bitmap);
         }
@@ -547,7 +547,7 @@ static void dirty_bitmap_load_complete(QEMUFile *f, DirtyBitmapLoadState *s)
         if (enabled_bitmaps == NULL) {
             /* in postcopy */
             bdrv_reclaim_dirty_bitmap_locked(s->bs, s->bitmap, &error_abort);
-            bdrv_enable_dirty_bitmap(s->bitmap);
+            bdrv_enable_dirty_bitmap_locked(s->bitmap);
         } else {
             /* target not started, successor must be empty */
             int64_t count = bdrv_get_dirty_count(s->bitmap);
-- 
2.14.4